Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

TL;DR

This study investigates the microwave properties of bulk MgB2 coaxial cavities, analyzing their surface resistance and quality factors at cryogenic temperatures and varying power levels, demonstrating stable performance up to high input powers.

Contribution

It presents the first detailed microwave characterization of bulk MgB2 coaxial cavities, including measurements of surface resistance and quality factors under different conditions.

Findings

MgB2 cavities exhibit low surface resistance at 4.2 K and 2.5 GHz.

Surface resistance remains stable up to 10 dBm input power.

Quality factor remains high and stable across a wide power range.

Abstract

We report on the microwave (mw) properties of coaxial cavities built by using bulk MgB2 superconductor prepared by reactive liquid Mg infiltration technology. We have assembled a homogeneous cavity, by using an outer MgB2 cylinder and an inner MgB2 rod, and a hybrid cavity by using an outer copper cylinder and the same MgB2 rod as inner conductor. By the analysis of the resonance curves, in the different resonant modes, we have determined the microwave surface resistance, Rs, of the MgB2 materials as a function of the temperature and the frequency, in the absence of DC magnetic fields. At T = 4.2 K and f = 2.5 GHz, by a mw pulsed technique, we have determined the quality factor of the homogeneous cavity as a function of the input power up to a maximum level of about 40 dBm (corresponding to a maximum peak magnetic field of about 100 Oe). Contrary to what occurs in many films, Rs of the MgB2 material used does not exhibit visible variations up to an input power level of about 10 dBm and varies less than a factor of 2 on further increasing the input power of 30 dB.